I was wondering why the feminine article is often used for "camel" (many times in the old testament; and also Matt 23:24 uses "την καμηλον"). Is that the default? Related to that, how did the LXX translators decide which gender to use (Lev 11:4, Deut 14:7 use "τον καμηλον")?

The fact that κάμηλος can be masculine or feminine without changing declension exhausts the Greek content of this question.

As for why the camel in Matt 23:24 is feminine, I consulted several commentaries and ... nothing. They don't even notice. If there's something particular about she-camels in this culture, I don't know what it is.